The present invention relates generally to optical safety filters. More specifically, the present invention relates to optical safety filters that provide laser protection across a plurality of narrowly selected wavelength ranges corresponding to laser emissions, while also including a color-balancing component that enhances the color rendering performance of the filter.
In a number of commercial and military fields there is a growing awareness that certain wavelengths of energy emissions are harmful to the eye. Generally, such energy emissions, in the form of a laser emission, are grouped at or around three wavelengths corresponding to approximately 400-1400 nm. For example, energy emitted from a laser operating in one of these wavelength ranges can cause both temporary and permanent blindness and can be disorienting to those people that have been exposed. The adverse effects of energy emissions having wavelengths within these wavelength regions are only recently beginning to be fully recognized as applications that utilize such energy emissions are more frequently employed. For example, there are a number of optical communication protocols that utilize lasers tuned to these wavelengths for the transmission of data as well as a number of military applications that employ infra-red and near infra-red laser energy emissions at these wavelengths in connection with the sighting of weapons and target acquisition. As the environments in which the use of such energy emissions increases, the potential for accidental exposure to such emissions also greatly increases.
In the past, to avoid accidental exposure to infra-red and visible laser emissions, people have attempted to protect their eyes through the use of nonselective filters that simply include a broad wavelength dark filter that screens out the potential for exposure to harmful emission levels. In this regard, however, the broadband filters reduce the magnitude of the exposure over a wider range than screening out the harmful wavelengths of energy. As a result, with only a few exceptions, such filters have generally been directed toward the reduction in intensity of the light transmitted, rather than to the filtering of any particular wavelength or group of wavelengths.
The problem with such a prior art approach is that the nonselective reduction in overall light transitivity generally impacts the visual acuity of the wearer making the use of such filtering difficult if not impossible to implement due to the severe limitations imposed on the visibility of the wearer. One key area that further limits the wearability of such generalized filters is traffic signal recognition. To meet the standards required for use as sunglasses, the wearer must be able to differentiate between red and green traffic signals. Often broad filters directed at screening the above laser energy emissions also result in severely limiting the wearer's ability to differentiate between red and green objects making traffic identification difficult if not impossible.
Another prior art approach involved in laser filtering related to the use of specialty lenses. The difficulty with such lenses is that they typically have a limited range of properties, because they are made of glass or high impact polymers such as polycarbonate, thereby requiring that the additives used to modify the transmissivity must be compatible with the high temperatures required in making the glass or molding of the polymer material. The range of substances that are available that are both compatible with the high molding temperatures and capable of imparting the desired filtering properties is very narrow and generally does not provide the versatility typically encountered with organic dyestuffs that are normally utilized for narrow wavelength filtering. An example of such a prior art filter is illustrated in the performance graph at FIG. 1. The curve illustrates a prior art optical filter tailored for filtering energy in the range of approximately 755 nm-1064 nm. As can be seen, the filter provides a filtering performance curve that exhibits filtering characteristics on the order of 5 optical density (OD) between the wavelengths of about 755 nm to about 1064 nm. In addition, however, the filter still exhibits filtering on the order of 2-3 OD for wavelengths as low as 700 nm and as high as 1080 nm. Since transmissivity is the inverse of OD to the base 10, this translates to a transmissivity of almost zero in the target filtering range of 755 nm-1064 nm with a visible light transmission (VLT) across the remaining spectrum of only around 30-35%. As can be seen, the results indicate a relatively low performance filter with a limited VLT value.
Should the above approach be taken to create a filter to cover all three of the identified energy emission ranges, a lens is produced that exhibits a very undesirable color. Not only is this undesirable from a commercial standpoint, it further encounters the problem that the filter does not allow the wearer to differentiate well between reds and greens. Finally, such a lens has a low light transmissivity because the overlap of the three broad filtering ranges needed to cover the target energy covers almost the entire visible spectrum.
As a result there is a need for an optical filter that blocks narrow bands of energy emissions corresponding laser energy emission while preserving the wearer's ability to differentiate between reds and greens. There is a further need for an optical filter that is molded from a polymer and includes dyes that filter laser energy emissions while having a pleasing overall color and while also preserving the wear's ability to differentiate between colors.